a) Field of the Invention
The invention is directed to a method for controlling a vacuum valve arranged between two vacuum chambers. The vacuum valve comprises a valve body with a valve opening, a closure member which closes the valve opening in a closed state of the vacuum valve and which releases the valve opening in an open state of the vacuum valve, wherein, for closing the valve opening by the closure member in the closed state of the vacuum valve at least one flexible seal contacts a sealing surface of the vacuum valve, which sealing surface is acted upon by a pressing force in the closed state of the vacuum valve, and further comprises an actuating device for opening and closing the vacuum valve with at least one actuator by which the seal is placed against the sealing surface by means of a displacement of the closure member for closing the vacuum valve, and with a control unit which controls this at least one actuator, pressure measurement values being supplied to this control unit as input signals from pressure sensors which detect the respective pressure in the two vacuum chambers. The invention is further directed to a vacuum valve of the kind mentioned above.
b) Description of the Related Art
Vacuum valves are known in different embodiment forms. For example, U.S. Pat. No. 4,052,036 and U.S. Pat. No. 4,470,576 disclose slide valves in which the flexible seal arranged at the valve plate is placed against a sealing surface arranged at the valve body in the closed state by spreading a valve plate.
U.S. Pat. No. 4,809,950 discloses a slide valve in which a circumferentially closed seal 2 has portions which are arranged at end faces of the closure member and which lie in planes that are offset relative to one another in direction of the longitudinal axis of the valve opening and are connected to one another by connection portions. In a slide valve of this type, a multiple-step movement sequence with movement components in different directions is not required to prevent shearing forces acting on the seal when the closure member is closed. A similar slide valve with a linear displacement of the closure member between its opened position and its closing position is known from U.S. Pat. No. 4,921,213. In this case, connection portions between portions of the circumferentially closed seal that are arranged at the end faces of the closure member extend parallel to a plane formed by the longitudinal axis of the valve opening and by the closing direction.
Butterfly valves are known from U.S. Pat. No. 4,634,094 and U.S. Pat. No. 6,494,434 B1. In these butterfly valves, the plate-shaped closure member is swiveled between its open position and its closing position around an axis which lies perpendicular to the longitudinal axis of the valve opening. In its open position, the valve disk is arranged in the valve opening.
U.S. Pat. No. 6,431,518 B1, for example, describes an L-valve in which the closure member is initially moved from its open position into a position located opposite from the valve opening in which it is lifted from the valve seat and is consequently placed against the valve seat in a movement substantially in direction of the longitudinal axis of the valve opening.
U.S. Pat. No. 5,577,707 discloses a slide valve in which the closure member comprises a valve plate and a closing ring which is displaceably supported at the valve housing. In the closed state of the vacuum valve, the closing ring is placed against the valve plate and a sealing ring of the closing ring contacts a sealing surface of the valve plate.
In another type of plate valve, also known as a pendulum valve, there is no linear displacement of the closure member in the first stage of the movement of the plate-shaped closure member but, rather, a swiveling along a circular arc so that the closure member is moved into the position opposite the valve opening. The second stage of the closing movement of the closure member in the direction of the valve seat is effected in that the closure member, which is located opposite the valve seat but is initially still lifted from the valve seat, is displaced in direction of the longitudinal axis of the valve opening.
Another known type of plate valve is the corner valve. In these corner valves, a valve rod to which the plate-shaped closure member is fixed is guided out of the vacuum through a wall located opposite from the valve opening by means of a suitable guide-through. The passage forming the valve opening through the valve body has two portions extending at an angle to one another.
All of these types of vacuum valves can be constructed in such a way that they can be opened and closed manually. Further, the actuation device of a valve of this type for opening and closing the closure member can comprise at least one actuator which is controlled by a control unit. Pneumatic piston-cylinder units in particular are used as actuators for vacuum valves. However, actuators formed by electric motors or electromagnetic units are also known.
In vacuum valves that can be closed by means of actuators, the full closing force of the actuator usually acts on the closure member in the closed state in order to press the seal against the sealing surface and close the valve in a vacuum-tight manner. In the vacuum valve in U.S. Pat. No. 6,629,682 B2, a flexible supporting ring is arranged, in addition to the flexible seal, at the closure member in order to limit the pressing force acting on the seal in a vacuum valve in which the closure member is pressed against the valve seat more or less firmly depending on the differential pressure acting on this closure member. This is intended to reduce wear on the seal, which increases as stress increases. The problem of wear on the seal is aggravated by the use of aggressive process gases. It has been established that the flexible materials that are usually used for the seals are chemically corroded by aggressive process gases particularly when they are under high stress.
For purposes of reducing wear on the seal, it has already been suggested to provide an attitude control or position control of the closure member in order to position this closure member at a given closing position by means of the actuator, so that the deformation of the flexible material of the sealing ring is limited to a predetermined value independent from the existing differential pressure.
Further, U.S. Pat. No. 6,367,770 B1 discloses a slide valve with a wedge-shaped closure member having, at both of its inclined side surfaces, seals which contact sealing surfaces of a wedge-shaped valve seat in the closed state of the valve. In the closed state of the valve, the closure member is moved into the valve seat only in such a way that the seals are substantially not pressed. Pressing of a seal is not carried out until a differential pressure acts upon the closure member and presses the closure member against one of the two sealing surfaces.